It is well known to use medical imaging techniques to obtain image data that is representative of structures within the body of a patient or other subject. It is known to perform angiography to image the blood vessels.
Traditionally, angiography has been in the form of catheter angiography, in which a catheter is inserted into a large vessel and navigated to the point of interest (for example, the heart), where a contrast agent is injected and multiple two-dimensional still images or short films are taken using X-ray fluoroscopy. In these images, the vessels may be seen clearly due to the contrast agent. Catheter angiography is an invasive process.
An alternative to catheter angiography is CT (computerized tomography) angiography. In CT angiography, a contrast agent is introduced into a blood vessel and a CT scan is then taken, in which multiple slices are combined to provide a three-dimensional image data set, with blood vessels highlighted by the contrast agent. CT angiography is considered one of the best tools to non-invasively analyze vessels for structural problems.
Other modalities of imaging are also possible, with or without the use of a contrast agent.
One form of structural problem that occurs in blood vessels is the formation of stenoses. A stenosis is an abnormal constriction or narrowing of a vessel. FIG. 1 is an image of a blood vessel showing two normal vessel regions 2 and two regions of stenosis 4. The regions of stenosis can be seen as narrowed sections of the vessel. Stenosis can manifest in different anatomical parts, for example coronary artery stenosis, renal artery stenosis or carotid artery stenosis.
It may be possible to manually identify stenoses on medical images of the blood vessels, assuming that a suitable view may be found in which the stenosis is apparent. However, it can be time-consuming and cumbersome. Choosing angles and measurement views is not straightforward, as visibility of the vessels and the ability to assess narrowing will change with angle. Additionally, manual identification and quantification can produce measurement results that are dependent on the user.
There exist methods that identify stenosis automatically within a given vessel section, but such methods are often complex and in some cases also require manual identification of the relevant vessel section by a user.